1. Field of the Invention
The present invention relates to a facsimile machine having an image memory.
2. Related Background Art
A conventional facsimile machine which carries out both memory transmission and half-tone (gray level) transmission, reads a transmission text, temporarily stores the read image information in a memory and then transmits it. In the conventional facsimile machine, the memory transmission is carried out whether a half-tone mode is selected or not.
On the other hand, when a half-tone image is encoded by using MH (modified Huffman) or MR (modified READ) which is a conventional G3 facsimile encoding system, image data may increase by a factor of several times than that in a non-compression mode. Accordingly, in the half-tone mode, the number of fill-bits is small and substantial reduction of communication time by the removal of the fill-bits is not to be expected.
Half-tone coding by a dither method increases a data length per line compared to that obtained with a binary image. In a CCITT G3 facsimile machine, if data is shorter than a minimum transmission time for one line, fill-bits (fill-data) are filled, i.e inserted, before the transmission to assure the minimum transmission time. In a memory communication, data is transferred between a memory of a communication unit and a memory of a receiver, and the, merit of the memory communication is that it is affected by a speed of a record unit (a unit which includes a motor) of the receiver, but in the memory transmission (communication), it is not affected and the speed is increased by transferring data with the fill-bits omitted.
In most cases of the half-tone encoding by the dither method, the data length for one line is longer than the minimum transmission time. Accordingly, there are few fill-bits in the half-tone encoding. Accordingly, there is little difference in speed of the half-tone image transmission between the conventional transmission and the memory transmission. Accordingly, in the half-tone mode, much is not expected for the reduction of communication time by the removal of the fill-bits.
In the conventional facsimile machine which carries out both the memory transmission and the half-tone transmission, if the memory transmission is carried out while the half-tone mode is selected, much reduction of the communication time is not expected. The memory transmission is disclosed in U.S. patent applications filed by the assignee of the present invention, Ser. Nos. 089,055, filed on Aug. 24, 1987, 755,361, filed on July 16, 1985 and 834,780, filed on Feb. 28, 1986. In U.S. patent application Ser. No. 665,353, filed on Oct. 26, 1984, data transmission is carried out without routing through the memory if the amount of data is large. In U.S. patent applications Ser. Nos. 082,977, filed on Aug. 4, 1987, and 014,077, filed on Feb. 3, 1987; data is not encoded but stored in a memory if amount of encoded data is larger than amount of original data.